Cloning is a technique used by custom layout designers (for instance, designers of analog solid-state semiconductor circuitry) to re-use existing layout, which is referred to herein as “source layout” or “source”. Such existing layout may include, for example, circuit elements such as field-effect transistors (FETs), which are defined in terms of geometries for the drain, gate and source, with connection points, etc. The geometries are used for semiconductor fabrication of the circuit elements.
Typically, a circuit design is expressed in the form of a schematic diagram, showing the elements (also called substructures) of the circuit, and their interconnections. For instance, a circuit schematic-level design might include multiple occurrences of a given type of FET. The elements or substructures are herein referred to as “targets”. In such a design including multiple occurrences of a circuit element such as the circuit elements (for instance, FETs) described above, each occurrence of the circuit element is placed, routed and optimized at a respective location within the schematic design.
Doing a design layout involves generating a design layout made up of semiconductor layouts of the circuit elements, with a connective topography the same as that given in the schematic diagram. Where the schematic diagram calls for multiple occurrences of a given circuit element, cloning involves using a semiconductor layout of the circuit element multiple times in the design layout.
Cloning typically involves three steps: (1) Define or extract a connectivity pattern of the source layout. (2) Identify sub structures (referred to herein as “targets”, “target elements” or “target components”) in the design whose functionality and connectivity pattern match that of the source layout. (3) For each identified sub structure, make a geometrical copy of the source layout, and update the copy's connectivity against the target, to be the same as the target.
In the past, such placement, routing and optimization has been done manually by the designer. More recently, designers have been able to employ a computer-based design layout system. Examples of such layout design systems include the Virtuoso Layout Suite XL product of Cadence Design Systems, Inc., and the Laker Layout Editor of SpringSoft, Inc.